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typestring.go
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typestring.go
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// Copyright 2013 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.
// This file implements printing of types.
package types
import (
"bytes"
"fmt"
)
// A Qualifier controls how named package-level objects are printed in
// calls to TypeString, ObjectString, and SelectionString.
//
// These three formatting routines call the Qualifier for each
// package-level object O, and if the Qualifier returns a non-empty
// string p, the object is printed in the form p.O.
// If it returns an empty string, only the object name O is printed.
//
// Using a nil Qualifier is equivalent to using (*Package).Path: the
// object is qualified by the import path, e.g., "encoding/json.Marshal".
//
type Qualifier func(*Package) string
// RelativeTo(pkg) returns a Qualifier that fully qualifies members of
// all packages other than pkg.
func RelativeTo(pkg *Package) Qualifier {
if pkg == nil {
return nil
}
return func(other *Package) string {
if pkg == other {
return "" // same package; unqualified
}
return other.Path()
}
}
// If gcCompatibilityMode is set, printing of types is modified
// to match the representation of some types in the gc compiler:
//
// - byte and rune lose their alias name and simply stand for
// uint8 and int32 respectively
// - embedded interfaces get flattened (the embedding info is lost,
// and certain recursive interface types cannot be printed anymore)
//
// This makes it easier to compare packages computed with the type-
// checker vs packages imported from gc export data.
//
// Caution: This flag affects all uses of WriteType, globally.
// It is only provided for testing in conjunction with
// gc-generated data.
//
// This flag is exported in the x/tools/go/types package. We don't
// need it at the moment in the std repo and so we don't export it
// anymore. We should eventually try to remove it altogether.
// TODO(gri) remove this
var gcCompatibilityMode bool
// TypeString returns the string representation of typ.
// The Qualifier controls the printing of
// package-level objects, and may be nil.
func TypeString(typ Type, qf Qualifier) string {
var buf bytes.Buffer
WriteType(&buf, typ, qf)
return buf.String()
}
// WriteType writes the string representation of typ to buf.
// The Qualifier controls the printing of
// package-level objects, and may be nil.
func WriteType(buf *bytes.Buffer, typ Type, qf Qualifier) {
writeType(buf, typ, qf, make([]Type, 0, 8))
}
func writeType(buf *bytes.Buffer, typ Type, qf Qualifier, visited []Type) {
// Theoretically, this is a quadratic lookup algorithm, but in
// practice deeply nested composite types with unnamed component
// types are uncommon. This code is likely more efficient than
// using a map.
for _, t := range visited {
if t == typ {
fmt.Fprintf(buf, "○%T", typ) // cycle to typ
return
}
}
visited = append(visited, typ)
switch t := typ.(type) {
case nil:
buf.WriteString("<nil>")
case *Basic:
if t.kind == UnsafePointer {
buf.WriteString("unsafe.")
}
if gcCompatibilityMode {
// forget the alias names
switch t.kind {
case Byte:
t = Typ[Uint8]
case Rune:
t = Typ[Int32]
}
}
buf.WriteString(t.name)
case *Array:
fmt.Fprintf(buf, "[%d]", t.len)
writeType(buf, t.elem, qf, visited)
case *Slice:
buf.WriteString("[]")
writeType(buf, t.elem, qf, visited)
case *Struct:
buf.WriteString("struct{")
for i, f := range t.fields {
if i > 0 {
buf.WriteString("; ")
}
if !f.anonymous {
buf.WriteString(f.name)
buf.WriteByte(' ')
}
writeType(buf, f.typ, qf, visited)
if tag := t.Tag(i); tag != "" {
fmt.Fprintf(buf, " %q", tag)
}
}
buf.WriteByte('}')
case *Pointer:
buf.WriteByte('*')
writeType(buf, t.base, qf, visited)
case *Tuple:
writeTuple(buf, t, false, qf, visited)
case *Signature:
buf.WriteString("func")
writeSignature(buf, t, qf, visited)
case *Interface:
// We write the source-level methods and embedded types rather
// than the actual method set since resolved method signatures
// may have non-printable cycles if parameters have anonymous
// interface types that (directly or indirectly) embed the
// current interface. For instance, consider the result type
// of m:
//
// type T interface{
// m() interface{ T }
// }
//
buf.WriteString("interface{")
empty := true
if gcCompatibilityMode {
// print flattened interface
// (useful to compare against gc-generated interfaces)
for i, m := range t.allMethods {
if i > 0 {
buf.WriteString("; ")
}
buf.WriteString(m.name)
writeSignature(buf, m.typ.(*Signature), qf, visited)
empty = false
}
} else {
// print explicit interface methods and embedded types
for i, m := range t.methods {
if i > 0 {
buf.WriteString("; ")
}
buf.WriteString(m.name)
writeSignature(buf, m.typ.(*Signature), qf, visited)
empty = false
}
for i, typ := range t.embeddeds {
if i > 0 || len(t.methods) > 0 {
buf.WriteString("; ")
}
writeType(buf, typ, qf, visited)
empty = false
}
}
if t.allMethods == nil || len(t.methods) > len(t.allMethods) {
if !empty {
buf.WriteByte(' ')
}
buf.WriteString("/* incomplete */")
}
buf.WriteByte('}')
case *Map:
buf.WriteString("map[")
writeType(buf, t.key, qf, visited)
buf.WriteByte(']')
writeType(buf, t.elem, qf, visited)
case *Chan:
var s string
var parens bool
switch t.dir {
case SendRecv:
s = "chan "
// chan (<-chan T) requires parentheses
if c, _ := t.elem.(*Chan); c != nil && c.dir == RecvOnly {
parens = true
}
case SendOnly:
s = "chan<- "
case RecvOnly:
s = "<-chan "
default:
panic("unreachable")
}
buf.WriteString(s)
if parens {
buf.WriteByte('(')
}
writeType(buf, t.elem, qf, visited)
if parens {
buf.WriteByte(')')
}
case *Named:
s := "<Named w/o object>"
if obj := t.obj; obj != nil {
if obj.pkg != nil {
writePackage(buf, obj.pkg, qf)
}
// TODO(gri): function-local named types should be displayed
// differently from named types at package level to avoid
// ambiguity.
s = obj.name
}
buf.WriteString(s)
default:
// For externally defined implementations of Type.
buf.WriteString(t.String())
}
}
func writeTuple(buf *bytes.Buffer, tup *Tuple, variadic bool, qf Qualifier, visited []Type) {
buf.WriteByte('(')
if tup != nil {
for i, v := range tup.vars {
if i > 0 {
buf.WriteString(", ")
}
if v.name != "" {
buf.WriteString(v.name)
buf.WriteByte(' ')
}
typ := v.typ
if variadic && i == len(tup.vars)-1 {
if s, ok := typ.(*Slice); ok {
buf.WriteString("...")
typ = s.elem
} else {
// special case:
// append(s, "foo"...) leads to signature func([]byte, string...)
if t, ok := typ.Underlying().(*Basic); !ok || t.kind != String {
panic("internal error: string type expected")
}
writeType(buf, typ, qf, visited)
buf.WriteString("...")
continue
}
}
writeType(buf, typ, qf, visited)
}
}
buf.WriteByte(')')
}
// WriteSignature writes the representation of the signature sig to buf,
// without a leading "func" keyword.
// The Qualifier controls the printing of
// package-level objects, and may be nil.
func WriteSignature(buf *bytes.Buffer, sig *Signature, qf Qualifier) {
writeSignature(buf, sig, qf, make([]Type, 0, 8))
}
func writeSignature(buf *bytes.Buffer, sig *Signature, qf Qualifier, visited []Type) {
writeTuple(buf, sig.params, sig.variadic, qf, visited)
n := sig.results.Len()
if n == 0 {
// no result
return
}
buf.WriteByte(' ')
if n == 1 && sig.results.vars[0].name == "" {
// single unnamed result
writeType(buf, sig.results.vars[0].typ, qf, visited)
return
}
// multiple or named result(s)
writeTuple(buf, sig.results, false, qf, visited)
}